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I was soundproofing my trunk and tire well when I noticed what looked like a bracket and mounting bolts for "something" in the forward-right side of the tire well. Later that afternoon, I stumbled across a picture of what I don't have in my trunk, while reading a tread about soundproofing. What is this thing with the red cables? Why doesn't my W212 have one? I have a 2010 E350, btw. Thanks for satisfying my curiosity.
Ha, yeah. It’s the auxiliary battery, for ECO start/stop.
I still would rather have a rocket launcher though.
I would agree it's an auxiliary battery, but Eco start/stop didn't happen til 2014. And the aux battery was typically in the side of the dash, not in the trunk. And before eco start/stop, the aux battery was for the transmission so you could still put it into a gear like neutral if the main battery died.
If anyone has a list of what this auxillary battery actually is responsible for controlling I would enjoy seeing it. I think there is much confusion as to why we have two batteries in our cars, unlike every other car on the planet with start/stop technology, remote start, etc. My 2019 Jeep Cherokee has all of this and more and works with one battery.
If anyone has a list of what this auxillary battery actually is responsible for controlling I would enjoy seeing it. I think there is much confusion as to why we have two batteries in our cars, unlike every other car on the planet with start/stop technology, remote start, etc. My 2019 Jeep Cherokee has all of this and more and works with one battery.
konigstiger has access to secret MB files and he post them sometimes.
I don't recall clear distinction what aux batter does, but very likely, just like in cars with SBC systems, it is booster battery. Meaning when the main battery goes low, some convenience items will turn off, cluster light will come on and car will drive some time using aux power.
It appears that this battery is for the ECO start/stop only. The reason for two batteries is still unclear, but appears that when the car STOPS the "active consumers" are switched over to the auxiliary battery , so that when the car STARTS there is no discernable break or "voltage dip" observed by the occupants. Ok, seems like a Mercedes over-engineer thing to me. There is no discernable "voltage dip" in my Jeep when starting during ECO mode.
Thank you Konigstiger! I have copied and filed.
I read the pdf konighstiger attached and even over the years I learned the hard way about electrical systems, the description operates with some electronic names as well, so I would have to spend several hr to research what it is about.
Main point I understood is that 2nd battery is to avoid power surge when you restart the engine.
The starting procedure is marvel on its own. It uses diesel injection, or spark ignition as main source, where starter is only helping source and I think it to avoid firing in reverse rpm.
My diesel when turned off, immediately drops rail pressure to about 10% on nominal and then it take like 2nd or 3rd cylinder turn to build the firing pressure.
When on ECO stop, the rail holds ca 5000 psi pressure (normal for idle) and engine is faster at operating speed than I can move my foot from brake to gas pedal.
Somehow I did not see the description saying about electric ATF pump, who keeps transmission ready to engage at any moment.
10-27-2019, 04:24 PM
